Digestors Designs

BIOGAS DIGESTORS ;

The many designs that are prevalent in the field. The designs may vary but the principle of digestion and methanisation remains the same . The tinkering has added to the overall efficiency of the plants of the days of Jasu Patel

Some Popular Indian Designs approved by MnRES and KVIC the nodal agency for Biogas

· KVIC : FDP with a cylinder digester
· Janta : FDP with a brick reinforced, moulded dome
· Pragati : FDP with a hemisphere digester
· Deenbandu : FDP with a hemisphere digester
· Ganesh : FDP made of angular steel and plastic foil
· FDP made of fiberglass reinforced polyester
· FDP made of pre-fabricated RCC compound

Sr. No.	Bio-gas Plants with Movable Gas holder	Fixed Dome Type	Plant Models	Flexible Bag Digester and gas holder Separate Plant
i	KVIC Design
ii	IARI Design	Sichuan Model	Sulabh Model	Neoprene Bag Model
iii	PRAI design (Two Chambers)	Shanghai Model	Bardoli Model	Swastik Biogas Plant
iv	Kamdhanu (baked clay) model	Janta (Brick Mesonry)	PAU Model	Red Mud Plastic Model
v	ASTRA Model	Bhagya Laxmi	Sangli Model
vi	JWALA Model	Kalinga (RCC)	CV Krishna Model (FRP Fixed Dome)
vii	Ganesh Model	ASTRA (Chinese type)
viii	Khira model	GAIC/ATRC (RCC segment) Model
ix	FRP Model	AFPRO (Horizontal RCC pipe ) model

China Fixed Dome

Fixed dome Chinese model biogas plant (also called drumless digester) was built in China as early as 1936. It consists of an underground brick masonry compartment (fermentation chamber) with a dome on the top for gas storage. In this design, the fermentation chamber and gas holder are combined as one unit. This design eliminates the use of costlier mild steel gas holder which is susceptible to corrosion. The life of fixed dome type plant is longer (from 20 to 50 years) compared to KVIC plant.

Comparison of KVIC and ASTRA designs For similar Biogas Plants

KVIC ASTRA

Rated daily gas output 5.66 5.66

Gas holder diameter (m 1.83 2.44

Gas holder height (m) 1.22 0.61

Gas holder volume ([m.sup.3]) 3.21 2.85

Digester diameter (m) 1.98 2.59

Digester depth (m) 4.88 2.44

Digester depth-diameter ratio 2.46 0.94

Digester volume ([m.sup.3]) 15.02 12.85

Capital cost of plant (Rs) 8,100.00 4,765.00

Relative costs 100.00 58.80

Daily loading (kg fresh dung) 150.00 150.00

Mean temperature (Celsius) 27.60 27.60

Daily gas yield ([m.sup.3]/day) 4.28 [+ -] 0.47 Capacity/rated capacity 75.6% 86.4%

Gas yield (cm/g fresh dung) 28.5 32.

Improvement in gas yield -- +14.2%

Janta

JANTA : Janata designs are relatively easy to construct and maintain because they have no moving parts and because corrosion is not a problem. One drawback is that Janata plants may require periodic cleaning due to scum build-up. As gas pressure increases in a fixed volume, the pressure pushes some of the slurry out of the digester and back into both the inlet and outlet tanks, causing the slurry level in each tank to rise.

DeenBandhu

Deenbandhu Model :The Deenbandhu Model is a semi continuous-fed fixed dome Biogas plant. The design essentially consists of segments of two spheres of different diameters joined at their bases. The structure thus formed comprises of (i) the digester (fermentation chamber), (ii) the gas storage chamber, and (iii) the empty space just above the gas storage chamber. The higher compressive strength of the brick masonry and concrete makes it preferable to go in for a structure that could be always kept under compression. A spherical structure loaded from the convex side will be under compression and therefore, the internal load will not have any effect on the structure.

KVIC Floating Drum

KVIC Design (Floating drum digester) Experiment on biogas technology in India began in 1937. In 1956, Jashu Bhai J Patel developed a design of floating drum biogas plant popularly known as Gobar Gas plant. In 1962, Patel's design was approved by the Khadi and Village Industries Commission (KVIC) of India and this design soon became popular in India and the world. In this design, the digester chamber is made of brick masonry in cement mortar. A mild steel drum is placed on top of the digester to collect the biogas produced from the digester. Thus, there are two separate structures for gas production and collection

JYOTI : This ensures that the heavier, partially digested material settles to the digester floor unimpeded by the lighter biomass. The JSEI innovation could be an important breakthrough in the use of agricultural and forest residues in biogas systems. In addition to solving the problem of scum build-up, the JSEI technique also seems to eliminate the necessity of excessive shredding or drying of residues, making the handling of these materials far less cumbersome and time-consuming. Biomass is merely chopped into 2-3 cm (.75-1.25") squares and then is pushed into the digester through a cylindrical tube inserted into the floating gas holder. The tube is always in contact with the slurry, even with the dome at maximum height, so that no gas can escap

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